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 A334980 a(n) is the total number of down steps between the (n-1)-th and n-th up steps in all 3_2-Dyck paths of length 4*n. A 3_2-Dyck path is a lattice path with steps (1, 3), (1, -1) that starts and ends at y = 0 and stays above the line y = -2. 5
 0, 3, 31, 248, 1941, 15334, 122915, 999456, 8231740, 68562887, 576661761, 4891506968, 41801697070, 359574305580, 3111012673755, 27055673506128, 236387476114548, 2073957836402524, 18264689865840284, 161403223665821280, 1430768729986730685, 12719497076318052990 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS For n = 1, there is no (n-1)-th up step, a(1) = 3 is the total number of down steps before the first up step. LINKS Michael De Vlieger, Table of n, a(n) for n = 0..1027 A. Asinowski, B. Hackl, and S. Selkirk, Down step statistics in generalized Dyck paths, arXiv:2007.15562 [math.CO], 2020. FORMULA a(0) = 0 and a(n) = 3*binomial(4*n+7, n+1)/(4*n+7) - 12*binomial(4*n+3, n)/(4*n+3) for n > 0. EXAMPLE For n = 2, the 3_2-Dyck paths are UDDDDDUD, UDDDDUDD, UDDDUDDD, UDDUDDDD, UDUDDDDD, UUDDDDDD, DUDDDDUD, DUDDDUDD, DUDDUDDD, DUDUDDDD, DUUDDDDD, DDUDDDUD, DDUDDUDD, DDUDUDDD, DDUUDDDD. Therefore the total number of down steps between the first and second up steps is a(2) = 5 + 4 + 3 + 2 + 1 + 0 + 4 + 3 + 2 + 1 + 0 + 3 + 2 + 1 + 0 = 31. MATHEMATICA a[0] = 0; a[n_] := 3*Binomial[4*n+7, n+1]/(4*n + 7) - 12 * Binomial[4*n + 3, n]/(4*n + 3); Array[a, 22, 0] PROG (SageMath) [3*binomial(4*n + 7, n + 1)/(4*n + 7) - 12*binomial(4*n + 3, n)/(4*n + 3) if n > 0 else 0 for n in srange(30)] # Benjamin Hackl, May 19 2020 CROSSREFS Cf. A334976, A334977, A334978, A334979. Sequence in context: A114654 A198151 A197231 * A111400 A057972 A221821 Adjacent sequences: A334977 A334978 A334979 * A334981 A334982 A334983 KEYWORD nonn,easy AUTHOR Sarah Selkirk, May 18 2020 STATUS approved

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Last modified August 7 21:19 EDT 2024. Contains 375017 sequences. (Running on oeis4.)